Connect VHF Hand-held to Boat Antenna

On another thread psneed made the point that antennas greatly influence radio performance and that provision to attach aVHF handheld to an installed high(er) gain antenna is a good backup comm device. I have occasionally thought about making this mod but never followed up. I searched TF and have been unsuccessful in finding anything specific as to how to do this. Probably a matter of nomenclature in my searches - I have to believe this subject has come up before.

In the dark and distant past, the USN taught me communications stuff - I have just enough retention to recall that impedance matches and such can be critical to radio/antenna performance. Is that a problem with this?

Further, I'm assuming this is only going to work if you have a screw-in or BNC connected antenna on the hand-held. I suspect the "waterproof" and "floating" hand helds are not candidates.

Thanks for the help.

sbu22 said:

On another thread psneed made the point that antennas greatly influence radio performance and that provision to attach aVHF handheld to an installed high(er) gain antenna is a good backup comm device. I have occasionally thought about making this mod but never followed up. I searched TF and have been unsuccessful in finding anything specific as to how to do this. Probably a matter of nomenclature in my searches - I have to believe this subject has come up before.

In the dark and distant past, the USN taught me communications stuff - I have just enough retention to recall that impedance matches and such can be critical to radio/antenna performance. Is that a problem with this?

Further, I'm assuming this is only going to work if you have a screw-in or BNC connected antenna on the hand-held. I suspect the "waterproof" and "floating" hand helds are not candidates.

Thanks for the help.

Click to expand...

Actually some or all of the waterproof models can be used as long as the rubber ducky is removable.

Just need an adapter either from the manufacturer or someplace...have seen them online...

We did exactly this when our primary radio at the lower helm was at Icom for trouble-shooting. The owner of the marine electronics shop we use made us up a short adapter cable that allowed our Icom handheld to be connected to the main radio's 24 foot antenna. One end of the adapter screws into the same connector the radio's stock short antenna screws into and the other end connects to the 24 foot antenna's co-ax that normally connects to the main radio.

While this did not alter the transmission strength--- the handheld is 5 watts as I recall--- it did extend the transmission and reception "reach" by virtue of the main antenna's height.

We used this setup for a couple of weeks while Icom tried to figure out the intermittent fault with our main radio and we had no communications problems at all.

Eventually, after freezing the main radio and baking it and giving it every other test they coiuld think of Icom gave up and gave us a brand new radio even though the one we'd sent in was out of warranty. The new one was an upgraded version of the one we'd sent in which was a nice bonus. We've saved the adapter in case we ever need to do this again.

not only just height...antenna db gain will improve transmission and reception in less than ideal conditions.

An antenna needs to be impedance matched to free space on one side and to the radio electronics on the other. A whip antenna ½ wavelength long is naturally matched to free space. They are usually fed with a 50 ohm coaxial cable with one of several standard connectors (BNC etc.), Most fixed mount radios have a 50 ohm input impedance so hooking up to an antenna is a simple matter of just using a length of coaxial cable with the appropriate connectors. There are adaptors that go from one type of coaxial connector to another. They are all about 50 ohms. A short antenna as found on a hand held requires additional matching to free space. This can be done either in the antenna itself or in the radio electronics. By unscrewing the “rubber ducky” you don’t really know what impedance you are seeing at the radio side so you can’t simply hook up a 50-ohm coax. The exception is if the hand held antenna is attached with a BNC connector. Then you know that the impedance at that point is 50 ohms and you can connect it to your fixed antenna via a coax cable. A rather long explanation, but you can improve the range of your handheld with a BNC antenna connector by connecting it to your higher gain and higher mounted fixed antenna. Marin's experience with the Icom was done by someone who knew what he was doing.

West Marine Advisor...............

Selecting a VHF Handheld Radio | West Marine

Antenna adapters connect your handheld to the ship’s antenna. This extends the range of the handheld dramatically, and is an important safety feature should your fixed radio fail. The type of adapter varies with the brand of radio: most use a BNC connector, while others use a special connector. All provide male PL-259 threads for connection to the antenna coax cable.

Marin's experience with ICOM (the company) tells me that they intend to be around for a long time and to sell everyone an ICOM radio. I've been partial to Standard, but this incident reinforces my sense that you can't go far wrong with ICOM, either.

psneed - thanks again - searching "VHF hand held antenna adaptor" were the key words needed. I'll take my chances with something over the counter and see how it goes.

Appreciate the good advice and discussion.

It is also good insurance to carry a stub "emergency"antenna that can attach to the back of your regular VHF.

Should the on board "real" antenna suffer a mishap, the tiny stub antenna will work , with limited range.

Many work better than the "real" antenna when it is laid down to go under opening bridges.

I keep a couple of these on board:

In a pinch, the handheld can be connected to one of the fixed-mount antenna cables.

FF makes a good point about being able to go the other way, and attach a small antenna to your fixed-mount VHF if needed.